Whether an electroluminescent device (for example, but not limited to OLED device) is a bottom emitting device or a top emitting device, there is an effect of resonant microcavity to some extent. The effect of resonant microcavity mainly refers to the redistribution of photon density in different energy states, so that only certain wavelengths of light meet the mode of the resonant microcavity can be emitted at a specific angle.
Therefore, in an electroluminescent device and a display device using an electroluminescence device, the intensity and color of the emitted light will change with the exit angle.
For example, whether an OLED is a bottom emitting device or a top emitting device, there is an effect of resonant microcavity to some extent. The cathode of a bottom emitting OLED device has high reflectivity, the anode of it has high transmittance, so the effect of resonant microcavity is not very significant; while the cathode of a top emitting OLED device is typically a translucent metal electrode, resulting in multi-beam interference; therefore the effect of resonant microcavity is significant. FIG. 1 shows a schematic diagram of the light intensity-angle distribution of the existing OLED device. Numerical values 0-1 are used to indicate the normalized light intensity. In the exit direction of the OLED device, the light intensity has a maximum value. The light intensity decreases gradually with the increase of the viewing angle. In the aspect of color, the existing OLED devices and various display devices (for example but not limited to liquid crystal displays) also have the similar viewing angle characteristics.
In order to improve the viewing angle characteristics, the common method is coating the light exit surface of the OLED device with a scattering layer, but the effect is limited.